In torque transmission systems, it is desired to monitor the output torque transmitted by the system, such as a gearbox, in order to prevent damage associated with a torque overload and/or provide feedback for control systems. Continuous torque monitoring of output torque is useful in various types of actuators, including actuators used for aircraft flight control systems and other applications.
One known approach for monitoring output torque is to measure strain on a rotating shaft using a torque sensor that rotates with the shaft. The measurement information generated by the rotating torque sensor must be transmitted via a slip ring or an electromagnetic field to a stationary receiver. Consequently, this approach is complex, costly, and unreliable.
Another known approach is to determine output torque by analyzing a pressure difference of a hydraulic drive motor or an energizing current of an electric drive motor, and then calculating the actual output torque by taking into account the gear efficiency and drag of the system. If the gear efficiency and drag of the system are not accurately known, or if they change due to variation in the operating conditions, accuracy of the calculated output torque will suffer.
A third known approach is to measure force at a mounting point of a component using strain gauges. This method is usually difficult to implement. Another drawback is that measurement signals generated by traditional strain gauge load sensing devices have large amounts of temperature error at warm and cold temperature extremes. Such temperature extremes are common, for example, in aircraft applications.
What is needed is a torque measurement system for a gearbox that is simple and economical to implement, and is highly accurate even when experiencing warm and cold temperature extremes.